The invention relates to a vapour compression device for a transcritical fluid cycle, comprising at least:                an internal heat exchanger,        a first vapour compression system connected to the outlet of the internal heat exchanger,        a first isobaric cooling system connected to the outlet of the first vapour compression system,        a fluid distributor placed at the outlet of first isobaric cooling system and separating the fluid into a main circuit of the cycle and an auxiliary cooling circuit of the cycle,        an auxiliary expansion system placed on the auxiliary cooling circuit between the fluid distributor and the inlet of the internal heat exchanger,        a main expansion system placed on the main circuit and connected to the outlet of the internal heat exchanger,        an evaporator operating at low pressure placed between the outlet of the main expansion system and the inlet of the internal heat exchanger.        
The invention also relates to a method of performing a transcritical fluid cycle between a hot source temperature and a cold source temperature by means of one such vapour compression device, comprising at least the steps of:                heating the fluid in the internal heat exchanger until the hot source temperature is reached,        compression of the fluid to reach a medium pressure and to reach the hot source temperature,        separation of the fluid by the fluid distributor into a main circuit of the cycle and an auxiliary cooling circuit of the cycle,        expansion of the fluid on the auxiliary cooling circuit by the auxiliary expansion system until the cold source temperature is reached,        expansion of the fluid on the main circuit by the main expansion system until the cold source temperature is reached,        isobaric evaporation of the fluid on the main circuit.        